1. Technical Field
The present disclosure relates to the field of electronics. In greater detail, the present disclosure relates to a diode.
2. Description of the Related Art
Diodes are electronic components widely used in various electronic circuits. For example, in the field of power electronics diodes (also referred to as high voltage diodes) are used for implementing rectifier circuits and protection circuits. For example, a particular application of diodes in the power electronics field is in switching mode power supplies (SMPS), such as flyback, buck, boost converters, etc., which are used to supply energy to circuits of various types (e.g., from data processing circuits to LED lighting systems); switching power supplies have a high efficiency and compactness compared with, for example, the classic power supplies simply comprising a ferromagnetic transformer.
Switching power supplies provide current and voltage at well-defined and stable values from a supply voltage (e.g., a main voltage) thanks to a high frequency switching (in the order of hundreds of KHz) between two or more operating conditions (e.g., an energy storing condition and an energy supplying condition). In particular, the energy conversion efficiency of the switching power supply increases with the switching frequency thereof. For this reason, in the art there is a continuous tendency to increase the switching frequency of the switching power supplies.
Therefore, the diodes used in switching power supplies (or more generally in any power electronics applications such as in insulated gate bipolar transistors (IGBT), power MOSFETs and thyristors) should be able to operate properly and with high performance at high frequencies.
Among high voltage diodes, the most widespread type is that known as PiN; a PiN diode comprises an anode region (P) of semiconductor material with p-type doping and a cathode region (N) of semiconductor material with n-type doping, between which a drift region (i) of semiconductor material with a weak n-type doping (lower than the n-type doping of the cathode) is interposed. Theoretically, the intermediate region of PiN diodes is an undoped intrinsic semiconductor region, hence the designation PiN, but PiN diodes are typically made using weak n-type doping in the intermediate/drift region. The drift region allows a correct operation even with high potential differences applied to the ends of the PiN diode (e.g., in the order of hundreds of Volts). In order to operate with high current intensity (e.g., in the order of tens of Amperes) the PiN diode is generally provided with a cellular-type structure with a plurality of anode regions electrically coupled but spaced apart one from the other.
The PiN diodes may have sub-optimal reverse recovery performance. In fact, when a control voltage of a PiN diode is switched from a forward biasing value to a shutdown or reverse biasing value, the charge carriers (electrons and holes) inside the drift region should be removed before the diode prevents a flow of electric current. This has a negative effect on a maximum switching frequency achievable by the PiN diode.
In order to increase the removal speed of the charge carriers of the PiN diodes (and hence the reverse recovery performance), in the art various changes to their structure have been proposed. In general, the known changes are based on introductions of recombination centers for the charge carriers in the drift region (called lifetime killing technique) and/or on variation of the structure of the anode and/or the cathode, e.g., buffer, Hybrid or ECPT (Collector Emitter Punch-Through) cathode structures and/or SSD (Static Shielding diode), MPS (Merged PiN Schottky diode), Speed (Self-Adjusting P-Emitter Efficiency diode), SFD (Soft and Fast Diode), ESD (Short Emitter Diode) and CIC (Charge Injection Control) anode structures.
However, the introduction of recombination centers generally increases leakage currents due to non-ideality of the PiN diodes. The solutions that modify the cathode structure generally increase a peak intensity of a reverse current generated during the reverse recovery phase. Finally, the solutions that modify the anode structure generally increase a threshold voltage required to activate the PiN diodes.